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Abstract
ObjectivesConventional scoring of sleep provides little information about the process of transitioning between vigilance states. We applied the state space technique (SST) using frequency band ratios to follow normal maturation of different sleep/wake states, velocities of movements, and transitions between states of juvenile (postnatal day 34, P34) and young adult rats (P71).Design24-h sleep recordings of eight P34 and nine P71 were analyzed using conventional scoring criteria and SST one week following implantation of telemetric transmitter. SST is a non-categorical approach that allows novel quantitative and unbiased examination of vigilance-states dynamics and state transitions. In this approach, behavioral changes are described in a 2-dimensional state space that is derived from spectral characteristics of the electroencephalography.Measurements and ResultsWith maturation sleep intensity declines, the duration of deep slow wave sleep (DSWS) and light slow wave sleep (LSWS) decreases and increases, respectively. Vigilance state determination, as a function of frequency, is not constant; there is a substantial shift to higher ratio 1 in all vigilance states except DSWS. Deep slow wave sleep decreases in adult relative to juvenile animals at all frequencies. P71 animals have 400% more trajectories from Wake to LSWS (p = 0.005) and vice versa (p = 0.005), and 100% more micro-arousals (p = 0.021), while trajectories from LSWS to DSWS (p = 0.047) and vice versa (p = 0.033) were reduced by 60%. In both juvenile and adult animals, no significant changes were found in sleep velocity at all regions of the 2-dimensional state space plot; suggesting that maturation has a partial effect on sleep stability.ConclusionsHere, we present novel and original evidence that SST enables visualization of vigilance-state intensity, transitions, and velocities that were not evident by traditional scoring methods. These observations provide new perspectives in sleep state dynamics and highlight the usefulness of this technique in exploring the development of sleep-wake activity.
Highlights
It has long been recognized that adequate sleep is fundamentally important for healthy growth, development, and homeostasis in human animals [1,2,3,4,5]
As a function of frequency, is not constant; there is a substantial shift to higher ratio 1 in all vigilance states except deep slow wave sleep (DSWS)
In both juvenile and adult animals, no significant changes were found in sleep velocity at all regions of the 2-dimensional state space plot; suggesting that maturation has a partial effect on sleep stability
Summary
It has long been recognized that adequate sleep is fundamentally important for healthy growth, development, and homeostasis in human animals [1,2,3,4,5]. Studies using traditional categorical sleep state scoring revealed that maturation can lead to increased wake time, decreased paradoxical sleep (PS), and decline of slow wave sleep (SWS) duration and power [13,14]. Several studies in rodents have reported an increase in wakefulness during puberty, which was complemented by a decrease in SWS and PS duration [15] and slow wave activity [14,16,17]. It was demonstrated that in the mouse cortex the observed developmental decrease in sleep slow wave activity cannot be accounted for by a net pruning of synapses [16]
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